Helicopter flight controls



July 12, 1966 H. H. REUTHER HELICOPTER FLIGHT CONTROLS 5 Sheets-Sheet 1 Filed May 28, 1964 INVENTOR HAROLD H. REUTHER BYfl/ -l M FIG. 2

ATTORNEY H. H. REUTHER HELICOPTER FLIGHT CONTROLS July 12, 1966 3 Sheets-Sheet 2 Filed May 28, 1964 INVENTOR HAROLD H. REUTHER BYAQ'ZLpQ W .H w k a FIG. 5

ATTORNEY July 12, 1966 REUTHER I 3,260,313

HELI COPTER FLIGHT CONTROLS Filed May 28, 1964 3 eet 5 [J 44 I J:

FIG. 6

INVENTOR HAROLD H. REUTHER BYM'L (a. M

ATTORNEY United States Patent 3,260,313 HELKIOPTER FLIGHT CONTROLS Harold H. Reuther, 1157 Cleveland Ave., Wyomissing, Pa.

Filed May 28, 1964, Ser. No. 370,943 2 Claims. (Cl. 170-16025) This invention relates to rotary wing aircraft of the type generally referred to as helicopters, and, more particularly, relates to improved systems for controlling the speed and direction of such aircraft in horizontal and vertical flight.

This invention is particularly concerned with helicopters of the type that, for convenience, may be referred to as those having their rotor blades mounted upon oblique axes. In this type of mounting, the root of each blade is attached to the rotor hub so that the major or longitudinal axis of the blade does not pass through the center of rotation of the rotor. This may be accomplished by hingedly securing the root of the blade to a rotor hub with the axis of the hinge oblique to the major axis of the blade. Preferably, this oblique angle should be about 45 when two or four blades are used in the rotor, but may be varied from this when an odd number of blades, such as three or five, are used.

By mounting the rotor blades on an oblique axis, rotation of the blades about the axis of the hinge will cause the blade to move in a compound motion. First, the angle between the plane of the blade and the normal plane of rotation (horizontal) will be changed. This angle is commonly referred to as the coning angle. Secondly, the blade will turn about its longitudinal axis to vary the pitch of the blade.

From-the above, it can be appreciated that both the pitch of the blades and their coning angle may be controlled simultaneously by means of rotating the roots of the blades about the axes of their hinge pins. Further, unlike more conventional helicopters, a positive control over the coning angle is obtained.

The use of an oblique axis for mounting rotor blades in connection with helicopters has been proposed for some time, and reference is made to British patent specification 360,494 filed in the name of Rudolph Chillingworth in which these broad principles are disclosed. While the designs of helicopters in patents such as this are basically sound, they have failed to achieve commercial success due,'in part, to the fact that suitable systems have not been designed for controlling such helicopters in horizontal and vertical flight.

Accordingly, it is a principal object of this invention to provide improved methods and means for controlling the horizontal and vertical flight of helicopters having their rotor blades mounted upon oblique axes.

Another object of this invention is to provide a helicopter in which positive control may be maintained over the coning angle of the blades.

Yet another object of this invention is to provide a helicopter having improved safety that in the event of complete loss of power will descend at a rate within certainlimitsof safety.

And yet another object of this invention is to provide a helicopter having rotor blades that may readily be detached for purposes of storage or inspection.

A still further object of this invention is to provide a helicopter with simplified control means that will make it easier for the pilot to control the helicopter in flight.

And a still further object of this invention is to provide a helicopter of simplified design and construction utilizing rotor blades mounted on oblique axes.

These and other objects of this invention will become 3,260,313 Patented July 12, 1966 apparent from the following description of the drawings.

In the drawings:

FIG, 1 is a schematic view, partially in section, showing a rotor and a drive assembly for use in a helicopter constructed in accordance with this invention.

FIG. 2 is a view in plan, partially cut away, showing ,a rotor hub and the root ends of two blades attached thereto.

FIG. 3 is a detail in section showing an alternative means for mounting blades in accordance with this invention.

FIG. 4 is a schematic view showing a suitable hydraulic control system for use in accordance with this invention.

FIG. 5 is a schematic drawing illustrating a simplified hydraulic system useful in the practice of this invention.

FIG. 6 is a schematic view of an alternative hydraulic control system for use in accordance with this invention.

FIG. 7 is a schematic representation of a rotor blade mounted on an oblique axis.

Referring first to FIG. 7, the principle of mounting a rotor blade on an oblique axis is illustrated. Here the blade b is shown with its major axis aa making an angle 0 with respect to the axis h-h of the hinge pin on which the blade is mounted for rotation. 'By these means, when the blade b is rotated about the axis h-h of the hinge pin, the front 0 and rear d edges of the blade tip traverse different distances during such rotation. Thus, rotation of the blade b about axis hh will cause the tip c to move more quickly than the tip d, and the angle of pitch will increase from the root toward the tlp of the blade as the blade is turned from its horizontal position. It will be appreciated that this action of providing a pitch to the blade occurs simultaneously with, and is superimposed upon, the major motion of the blade that results in establishing a coning angle as the blade b is rotated about axis hh.

When the pitch of all of the rotor blades is changed to the same extent and in the same direction, it is referred to as collective pitch. Control of collective pitch is essential (in addition to rotor speed) to control the vertical movement of the helicopter as by causing it to rise when the collective pitch is increased or to hover or descend when it is reduced.

In addition, in order to obtain horizontal motion of the helicopter, provision is made to alter the pitch of each of the blades consecutively from a minimum to a maximum during each revolution of the rotor. This is referred to as cyclic pitch. The cyclic pitch is superimposed upon the collective pitch of the blades in order that the total lift force will remain substantially unchanged.

In accordance with this invention, control over the cyclic pitch is obtained by means of a swash plate as best illustrated in FIG. 1. Here the swash plate 1 is shown as being divided into an upper rotating disc 3 that can tilt in any direction and also rotate with the rotor and carry the roots of the blades 15 with it. The lower stationary disc 2 of the swash plate 1 does not rotate and can only tilt. A bearing race 4 is provided with ball bearings to separate the upper 3 and lower 2 discs of the swash plate 1, thus enabling the upper disc 3 to rotate freely relative to the lower disc 2.

The under surface of the lower disc 2 is supported by three or four hydraulic cylinders 6 (only two can be seen in FIG. 1). Piston rods 7 of the cylinders 6 are attached via a pivotable linkage 8 in supporting relationship with the under surface of the lower disc 2. The hydraulic cylinders 6 are, in turn, attached to a pivotable linkage 9 that is fixedly attached to the frame 11 of the helicopter.

It will be appreciated that the lower disc 2 of the swash plate 1 may be made to assume any desired attitude by control of the piston rods 7.

A rotor hub 12 is provided that is fixedly attached to power shaft 19 as by nut 12a. The rotor hub 12 forms a support for the rotor blades at their root ends where the blades are attached via hinge pins 13 and an extension of the bladeroot 14 The control rod 14 passes through a ball and socket type bearing 16 mounted in the upper disc 3 of the swash plate 1 to enable both rotation and axial displacement of the control rod with respect to the ball and socket bearing 16. An operating power shaft 19 passes through a sleeve bearing 18 that, in turn, supports the ball and socket bearing 17 of the upper rotating disc 3, the ball race 4, and the ball and socket type bearing of the lower stationary disc 2. The sleeve 18 is retained in position at its lower end by means of a nut 18a and at its upper end by means of nut 18b. A sleeve bearing 21 is .also provided around the operating power shaft 19 adjacent where the shaft 19 passes through the helicopter frame 11. Note that by this arrangement, power may be transmitted from the gearing 22 directly to the rotor hub 12 which in turn will cause the rotor blades 15 to turn, as well as the upper rotating disc 3.

A motor 24 is provided and, for convenience and space saving, may be of the radial or pancake type with its drive shaft in a vertical plane. Power from the engine 24 is transmitted to the gearing 22 by means of gear box 23.

As shown in FIG. 1, the piston rods 7 are in their fully extended positions which positions the upper rotating disc 3 in its uppermost position due to the fact that nut 18b is forced into abutting relationship with the underside of rotor hub 12. In the preferred design, when the upper disc 3 is in this position, the rotor blades 15 will have a slight coning angle and pitch in order that in the event of power failure, the collective pitch of the blades will slow the descent of the helicopter to the ground within certain limits of safety. When, however, piston rods 7 are retracted by the action of the hydraulic cylinders 6, the lower disc 2 will be lowered. and due to the forces acting upon the rotor blades, the movement of disc 2 will be followed by the upper rotating disc 3. As rotating disc 3 moves downward, it will carry with it the extensions 14 on the roots of the blade which, in turn, will cause the blades 15 to rotate about the axis of the hinge pins 13. The result of this rotation, as discussed above, will be to cause the blades 15 to assume a greater coning angle as well as to increase the pitch of the blades 15.

Still further, if the piston rods 7 are not all moved to the same degree or in the same direction, the lower disc 2 will assume a position inclined to the horizontal. As the upper disc 3 will follow the lower disc 2, the cyclic pitch of the blades is so controlled and control of the motion of the helicopter in horizontal directions is obtained.

Details as to the means for mounting rotor blades 15 on the hub 12 are best shown in FIG. 2. Note that by simply loosening nuts 13a and removing the hinge pins 13, the rotor blades 15 conveniently may be removed, either for storage or inspection.

In FIG. 3, a slightly different form of attachment of the rotor blades is shown. Here the ball and socket type bearing 16 of FIG. 2 is functionally replaced by a tongue 3a extending from the upper rotating disc 3. This tongue 3a is adapted to engage a grooved portion 14a that is formed on the extension 14 of the root end of the rotor blade 15.

Preferred means for controlling the attitude of the swash plate are shown somewhat schematically in FIG. 4 in which three hydraulic cylinders and their piston rods 7 are positioned to support the swash plate (not shown). Hydraulic control valves 71 are provided so that when their operating valve stems 69 are properly positioned, they will introduce high pressure hydraulic fluid to flow via lines 73 to the underside of pistons 7a while hydraulic fluid simultaneously is relieved from the upper side of pistons 7a via lines 72. When the operating valve stem 69 is moved to another position, the high pressure hyas shown in FIG. 4.

draulic fluid will then be introduced into the upper side of the piston 7a via line 72 and exhausted from the under side of the pistons 7a via hydraulic line 73.

As shown in FIG. 4, the three hydraulic control valves 71 are operated by manipulation of control stick 60. This control stick 60 is adapted for manual operation by the pilot of the helicopter and is supported in a universal joint 61 that permit the stick 6%) to be moved in a full arc of 360. Levers 62 are pivotally engaged at one of their ends with control stick 60 and at their other ends with cranks 63. Cranks 63 are pivotally engaged with control level 64 by means of pivots 68. Accordingly, when the crank 63 is actuated through the motion of levers 62 and control stick 60, the control levers 64 are caused to pivot around their fixed fulcrums 66 which, in turn, will cause the valve stems 69 of control valves 71, by means of the pivotal attachment 67, to move with respect to the body of valves 71. Thus, hydraulic control over the motion of piston rods 7 is obtained and the swash plate may be caused to assume the desired attitude to direct the flight of the helicopter.

Note, however, that if the control lever 60 is rotated about its own axis while substantially in a vertical position, all of the control valves 71 will be acted upon in the same direction and to the same degree. This will cause the piston rods 7 to move the same distance and in the same direction without affecting the attitude of the swash plate to the horizontal. As can be best appreciated by reference to FIG. 1, such upwardly and downwardly motion of the swash plate will cause the blades of the helicopter to pivot about their hinge pins 13, thus changing both the collective pitch and the coning angle of the blades. It can be appreciated that as the swash plate moves down, the coning angle and pitch of the blades will increase, and as the swash plate is moved up, the coning angle and pitch will be lessened. As previously noted, the swash plate preferably is prevented from moving to so high a vertical position as to result in a negative pitch or coning angle of the blades.

If the control stick 60, rather than being rotated about its own vertical axis, is moved in any direction displacing it from the vertical, it will, through the above described linkages, simultaneously move, to greater and lesser degrees, the various valve stems 69. This in turn will induce various degrees and directions of motion of the piston rods 7 which will enable positioning the swash plate 1, within limits, at any desired angle to the horizontal.

A control system as here shown in FIG. 4 is particularly advantageous due to the simplicity of construction and operation. As discussed above, complete control over both the collective pitch of the rotor blades and the coning angle is obtained by twisting the operating stick about its elongated axis. Further, by displacing the operating stick from its vertical position, the attitude of the swash plate can be controlled in order to change the cyclic pitch and, accordingly, the horizontal direction of the flight of the helicopter. As these manipulations require only the use of one hand of the pilot, considerable freedom is given to him to conduct other activities, such as operating cameras, ordinance equipment, and other auxiliary devices.

Another hydraulic systemv for controlling the attitude of the swash plate and, accordingly, both the collective and cyclic pitch of the rotor blades is shown in FIG. 6. Here the lower disc 2 of the swash plate 1 is shown supported by piston rods 7 of hydraulic cylinder 6. It should be understood that in this FIG. 6, for clarity, only one cylinder and one valve operating mechanism is shown, whereas in actuality there would be at least three present (Only two cylinders may be required if the swash plate is mounted in gimbals.) As all three cylinders are operated in an identical manner, a description with respect to only one of them will be sufficient fully to describe this modification of the invention.

Control stick 30 is mounted within the cockpit of the helicopter by suitable mounting means such as a universal joint 30a that enables movement of the stick through a full 360 arc. The motion of the stick 30 is transmitted via a lever 31, ball joint 31a and linkage 31b, to an operating lever 36. Operating lever 36 is pivoted for retation around a fulcrum 32 andis pivotally engaged with linkage 31b at pivot point 33 at one end, and is pivotally engaged with valve stem 37 at pivot 34 at its other end. Operating valve stem 37 controls the positioning of the valves with control valve 38. Control valve 38 is provided with a source of high pressure hydraulic fluid via line 39 and means to exhaust spent hydraulic fluid to a sump via line 41. Also, hydraulic lines 47 and 48 are connected to control valve 38 to conduct hydraulic fluid to and from hydraulic cylinder 6. Hydraulic line 48 communicates with the underside of piston 7a and hydraulic line 47 communicates with the upper side of piston 7a.

A bracket 42 is fixedly attached to piston rod 7 and, by means of an adjustment nut 43, is attached to feedback cable 44. Feedback cable 44 is attached at its lower end to a rigid rod 45 that is supported within a guide housing 46. Guide housing 46, in turn, is fixedly attached to the frame of the helicopter.

The control valve 38 is fixedly mounted upon and supported by a support plate 49. As is indicated in the drawing, support plate 49 may be moved upwardly or downwardly at the will of the operator by any convenient means, not shown. In operation, the control system such as shown in FIG. 6 will operate as follows. When the pilot moves the control stick 30 to a forward position, the lever 31 is moved in an upwardly direction and, acting through joint 31a and linkage 31b, causes lever 36 to pivot around fulcrum 32. This, in turn, causes pivot 34 to move downwardly carrying with it valve stem 37. This will uncover the port at the bottom of hydraulic lines 47 and 48. Oil under pressure will then enter control valve 38, pass through hydraulic line 48 and enter hydraulic cylinder 6 on the bottom side of piston 7a. Simultaneously, the return oil line 41 is placed in communication with hydraulic line 47, enabling hydraulic fluid to pass from the top side of piston 7a through hydraulic line 47 into and through control valve 38 and, via conduit 41, to the sump for the hydraulic fluid. It will be appreciated that by introducing high pressure hydraulic fluid on the bottom of piston 7a and relieving it on the top, piston 7a and its piston rod 7 will move in an upwardly direction, thus displacing its point of contact with the lower disc 2 of the swash plate, causing the disc 2 to assume a different attitude. At the same time, a negative feedback control is provided by means of feedback cable 44. As piston rod 7 moves upward, it carries with it bracket 42, cable 44 and rigid member 45. The effect of this is to move the fulcrum 32 about which lever 36 rotates and return operating valve stem 37 to a neutral position in which the ports of control valve are shut both with respect to hydraulic lines 47 and 48.

While not necessary to this invention, provision for a negative feedback means may be advantageous, as it makes it possible to position the control stick in a position that will correspond to the attitude that it is desired for the swash plate to assume. It is not necessary to return the control lever to its neutral position after the desired positioning of the swash plate has taken place, but rather it may be left in a position reflecting the position of the swash plate.

It will be appreciated that since three or four sets of levers 31, control valves 38 and hydraulic cylinders 6 are provided, all three or four hydraulic cylinders will be actuated to varying degrees and in appropriate directions when control lever 30 is moved. By this means the swash plate is given an appropriate attitude with respect to the horizontal in order that the cyclic pitch and horizontal flight of the helicopter may be maintained.

Additionally, it is, of course, necessary to adjust collective pitch and coning angle of the blades by adjusting the vertical position of the swash plate. To accomplish this, it is desirable to provide means for actuating all three or four piston rods 7 in the same direction and to the same degree simultaneously. This may be done by controlling the vertical position of valve support plate 49. As can be seen, as the valve support plate 49 is moved in an upwardly direction, the control valve body 38 will be displaced upwardly with respect to the operating valve stem 37, causing high pressure hydraulic fluid to flow into conduit 48 to the underside of piston 7a while hydraulic fluid simultaneously is relieved from the upper side-of piston 7a and returned to the sump via conduit 47. This, of course, will cause all of the piston rods 7 to react in an upwardly direction and, via the aforementioned feed-back circuit, the fulcrums 32 will be displaced upward, carrying with them operating valve stems 37, thus securing the flow of oil through hydraulic lines 47 and 48.

In FIG. 5, the elements of the hydraulic system of this invention are schematically illustrated wherein a single control valve 75 and a single hydraulic cylinder 6 are shown. A hydraulic pump P is driven by a motor M to pump oil from a sump S to a hydraulic accumulator A wherein the hydraulic fluid is stored at high pressure. When the valve 75 is properly positioned, high pressure hydraulic fluid will flow from the accumulator A to either the upper or lower side of piston 7a and exhaust from the other side of the piston 7a to the sump S. This will, of course, result in movement of piston rod 7. The returned hydraulic fluid is then stored in sump S until the pump P is again activated, causing the cycle of operation to repeat.

I claim:

1. A helicopter having a rotor hub and rotor blades carried thereby, the root of said blades being hinged to said hub on an axis oblique to the axis of the blade, a swash plate adjacent said hub, extensions on the roots of said blades forming means of attachment to said swash plate; said swash plate comprising a coaxially arranged tiltable, rotatable upper member, a tiltable non-rotatable lower member and a low friction bearing means positioned between said members; hydraulic means for inducing vertical movement of said lower member and inclining said last named member to a horizontal plane; said hydraulic means comprising a plurality of hydraulic pistons afiixed to a supporting plate mounted on the frame of the helicopter; said cylinders having piston rods extending therefrom and into contact with the lower side of said lower member of said swash plate; hydraulic control means for selectively moving said piston rods in a substantially vertical direction; said hydraulic control means including a series of valve means operatively connected to a flight control stick; said control means further including levers pivotally connected at one of their ends to said valve means and pivotally connected at the other of their ends to an operating crank extending from said flight control stick; said levers being supported for rotation in fulcrums positioned between their said ends; and means connecting each of said fulcrums with its respective piston rod to move directly therewith and with said swash plate.

2. A helicopter as set forth in claim 1 wherein the said supporting plate is movable toward and from said fulcrum.

References Cited by the Examiner UNITED STATES PATENTS Re. 22,595 1/1945 Upson l70l60.25 X 2,012,988 9/1935 Chillingworth l70160.57 2,133,043 10/1938 Rothenhoelfer l70-160.25 2,233,747 3/1941 Riedl l70160.27 X 2,384,445 9/1945 Apostolescu l60.25 2,495,523 1/1950 Hays 170160.26 X. 2,512,461 6/1950 Jenny 170l60.25 2,550,538 4/1951 Doman.

(Other references on following page) 7, UNITED STATES PATENTS 2/1953 Reuther 170-160.47 X 1/1960 Hook 170160.25

FOREIGN PATENTS 7/1926 Germany. 3/1941 Germany.

8 OTHER REFERENCES SAMUEL LEVINE, Primary Examiner.

5 JULIUS E. WEST, Examiner.

E. A. POWELL, IR., Assistant Examiners. 

1. A HELICOPTER HAVING A ROTOR HUB AND ROTOR BLADES CARRIED THEREBY, THE ROOT OF SAID BLADES BEING HINGED TO SAID HUB ON AN AXIS OBLIQUE TO THE AXIS OF THE BLADE, A SWASH PLATE ADJACENT SAID HUB, EXTENSIONS ON THE ROOTS OF SAID BLADES FORMING MEANS OF ATTACHMENT TO SAID SWASH 